AbstractWe surveyed 792 larval and 12,400 adult Coquillettidia perturbans for mermithid nematodes in 1990. Collections were made from cattail marshes in the greater Boston area. No mermithids were found in the adult mosquitoes, nor in larvae collected in mid-season, but 3 were found in larvae collected during September and October. This is only the second recorded occurrence of mermithids in Cq. perturbans.